[ARM] Skip debug during vpt block creation

[dmgreen]

Summary

Debug info is currently preventing VPT block creation, leading to different codegen. This patch attempts to skip any debug instructions during vpt block creation, making sure they do not interfere.

[samtebbs]

Very nice

llvm/lib/Target/ARM/MVEVPTBlockPass.cpp

static bool StepOverPredicatedInstrs(MachineBasicBlock::instr_iterator &Iter,
                                      MachineBasicBlock::instr_iterator EndIter,
                                      unsigned MaxSteps,
                                      unsigned &NumInstrsSteppedOver) {
   ARMVCC::VPTCodes NextPred = ARMVCC::None;
   Register PredReg;
   NumInstrsSteppedOver = 0;
 
   while (Iter != EndIter) {
+    if (Iter->isDebugInstr()) {
+      // Skip debug instructions
+      ++Iter;
+      continue;
+    }
+
     NextPred = getVPTInstrPredicate(*Iter, PredReg);
     assert(NextPred != ARMVCC::Else &&
            "VPT block pass does not expect Else preds");
     if (NextPred == ARMVCC::None || MaxSteps == 0)
       break;
     --MaxSteps;
     ++Iter;
     ++NumInstrsSteppedOver;
CreateVPTBlock(MachineBasicBlock::instr_iterator &Iter,
   LLVM_DEBUG(dbgs() << "VPT block created for: "; Iter->dump());
 
   unsigned BlockSize;
   StepOverPredicatedInstrs(Iter, EndIter, 4, BlockSize);
 
   LLVM_DEBUG(for (MachineBasicBlock::instr_iterator AddedInstIter =
                       std::next(BlockBeg);
                   AddedInstIter != Iter; ++AddedInstIter) {
+    if (AddedInstIter->isDebugInstr())
+      continue;
     dbgs() << "  adding: ";
     AddedInstIter->dump();
   });
 
   // Generate the initial BlockMask
   ARM::PredBlockMask BlockMask = GetInitialBlockMask(BlockSize);
 
   // Remove VPNOTs while there's still room in the block, so we can make the
if (!StepOverPredicatedInstrs(VPNOTBlockEndIter, EndIter, (4 - BlockSize),
       break;
 
     // Check if this VPNOT can be removed or not: It can only be removed if at
     // least one of the predicated instruction that follows it kills or sets
     // VPR.
     if (!IsVPRDefinedOrKilledByBlock(Iter, VPNOTBlockEndIter))
       break;
 
-    LLVM_DEBUG(dbgs() << "  removing VPNOT: "; Iter->dump(););
+    LLVM_DEBUG(dbgs() << "  removing VPNOT: "; Iter->dump());
 
     // Record the new size of the block
     BlockSize += ElseInstCnt;
     assert(BlockSize <= 4 && "Block is too large!");
 
     // Record the VPNot to remove it later.
     DeadInstructions.push_back(&*Iter);
     ++Iter;
 
     // Replace the predicates of the instructions we're adding.
     // Note that we are using "Iter" to iterate over the block so we can update
     // it at the same time.
     for (; Iter != VPNOTBlockEndIter; ++Iter) {
+      if (Iter->isDebugInstr())
+        continue;
+
       // Find the register in which the predicate is
       int OpIdx = findFirstVPTPredOperandIdx(*Iter);
       assert(OpIdx != -1);
 
       // Change the predicate and update the mask
       Iter->getOperand(OpIdx).setImm(CurrentPredicate);
       BlockMask = expandPredBlockMask(BlockMask, CurrentPredicate);
 

llvm/test/CodeGen/Thumb2/mve-vpt-block-debug.mir

bb.0.entry:
     ; CHECK: liveins: $q0, $q1, $q2
     ; CHECK: DBG_VALUE $q0, $noreg, !17, !DIExpression(), debug-location !21
     ; CHECK: DBG_VALUE $q0, $noreg, !17, !DIExpression(), debug-location !21
     ; CHECK: DBG_VALUE $q1, $noreg, !18, !DIExpression(), debug-location !21
     ; CHECK: DBG_VALUE $q1, $noreg, !18, !DIExpression(), debug-location !21
     ; CHECK: DBG_VALUE $q2, $noreg, !19, !DIExpression(), debug-location !21
     ; CHECK: DBG_VALUE $q2, $noreg, !19, !DIExpression(), debug-location !21
     ; CHECK: DBG_VALUE $noreg, $noreg, !20, !DIExpression(), debug-location !21
-    ; CHECK: BUNDLE implicit-def $vpr, implicit-def $q2, implicit-def $d4, implicit-def $s8, implicit-def $s9, implicit-def $d5, implicit-def $s10, implicit-def $s11, implicit $q1, implicit $q0, implicit killed $q2, debug-location !23 {
-    ; CHECK:   MVE_VPTv4s32 8, renamable $q1, renamable $q0, 10, implicit-def $vpr, debug-location !23
+    ; CHECK: BUNDLE implicit-def dead $vpr, implicit-def $q2, implicit-def $d4, implicit-def $s8, implicit-def $s9, implicit-def $d5, implicit-def $s10, implicit-def $s11, implicit killed $q1, implicit killed $q0, implicit killed $q2, debug-location !23 {
+    ; CHECK:   MVE_VPTv4s32 12, renamable $q1, renamable $q0, 10, implicit-def $vpr, debug-location !23
     ; CHECK:   renamable $q2 = MVE_VADDi32 renamable $q0, renamable $q1, 1, internal renamable $vpr, killed renamable $q2, debug-location !23
-    ; CHECK: }
-    ; CHECK: DBG_VALUE $noreg, $noreg, !20, !DIExpression(), debug-location !21
-    ; CHECK: DBG_VALUE $q2, $noreg, !19, !DIExpression(), debug-location !21
-    ; CHECK: renamable $vpr = MVE_VPNOT killed renamable $vpr, 0, $noreg, debug-location !24
-    ; CHECK: BUNDLE implicit-def $q2, implicit-def $d4, implicit-def $s8, implicit-def $s9, implicit-def $d5, implicit-def $s10, implicit-def $s11, implicit killed $vpr, implicit killed $q0, implicit killed $q1, implicit killed $q2, debug-location !25 {
-    ; CHECK:   MVE_VPST 8, implicit $vpr, debug-location !25
-    ; CHECK:   renamable $q2 = MVE_VADDi32 killed renamable $q0, killed renamable $q1, 1, killed renamable $vpr, killed renamable $q2, debug-location !25
+    ; CHECK:   DBG_VALUE $noreg, $noreg, !20, !DIExpression(), debug-location !21
+    ; CHECK:   DBG_VALUE internal $q2, $noreg, !19, !DIExpression(), debug-location !21
+    ; CHECK:   renamable $q2 = MVE_VADDi32 killed renamable $q0, killed renamable $q1, 2, internal killed renamable $vpr, internal killed renamable $q2, debug-location !25
+    ; CHECK:   DBG_VALUE internal $q2, $noreg, !19, !DIExpression(), debug-location !21
     ; CHECK: }
-    ; CHECK: DBG_VALUE $q2, $noreg, !19, !DIExpression(), debug-location !21
     ; CHECK: $q0 = MVE_VORR killed $q2, killed $q2, 0, $noreg, undef $q0, debug-location !26
     ; CHECK: tBX_RET 14 /* CC::al */, $noreg, implicit $q0, debug-location !26
     DBG_VALUE $q0, $noreg, !17, !DIExpression(), debug-location !21
     DBG_VALUE $q0, $noreg, !17, !DIExpression(), debug-location !21
     DBG_VALUE $q1, $noreg, !18, !DIExpression(), debug-location !21
     DBG_VALUE $q1, $noreg, !18, !DIExpression(), debug-location !21
     DBG_VALUE $q2, $noreg, !19, !DIExpression(), debug-location !21
     DBG_VALUE $q2, $noreg, !19, !DIExpression(), debug-location !21